/* The ziplist is a specially encoded dually linked list that is designed
 * to be very memory efficient. It stores both strings and integer values,
 * where integers are encoded as actual integers instead of a series of
 * characters. It allows push and pop operations on either side of the list
 * in O(1) time. However, because every operation requires a reallocation of
 * the memory used by the ziplist, the actual complexity is related to the
 * amount of memory used by the ziplist.
 *
 * ----------------------------------------------------------------------------
 *
 * ZIPLIST OVERALL LAYOUT:
 * The general layout of the ziplist is as follows:
 * <zlbytes><zltail><zllen><entry><entry><zlend>
 *
 * <zlbytes> is an unsigned integer to hold the number of bytes that the
 * ziplist occupies. This value needs to be stored to be able to resize the
 * entire structure without the need to traverse it first.
 *
 * <zltail> is the offset to the last entry in the list. This allows a pop
 * operation on the far side of the list without the need for full traversal.
 *
 * <zllen> is the number of entries.When this value is larger than 2**16-2,
 * we need to traverse the entire list to know how many items it holds.
 *
 * <zlend> is a single byte special value, equal to 255, which indicates the
 * end of the list.
 *
 * ZIPLIST ENTRIES:
 * Every entry in the ziplist is prefixed by a header that contains two pieces
 * of information. First, the length of the previous entry is stored to be
 * able to traverse the list from back to front. Second, the encoding with an
 * optional string length of the entry itself is stored.
 *
 * The length of the previous entry is encoded in the following way:
 * If this length is smaller than 254 bytes, it will only consume a single
 * byte that takes the length as value. When the length is greater than or
 * equal to 254, it will consume 5 bytes. The first byte is set to 254 to
 * indicate a larger value is following. The remaining 4 bytes take the
 * length of the previous entry as value.
 *
 * The other header field of the entry itself depends on the contents of the
 * entry. When the entry is a string, the first 2 bits of this header will hold
 * the type of encoding used to store the length of the string, followed by the
 * actual length of the string. When the entry is an integer the first 2 bits
 * are both set to 1. The following 2 bits are used to specify what kind of
 * integer will be stored after this header. An overview of the different
 * types and encodings is as follows:
 *
 * |00pppppp| - 1 byte
 *      String value with length less than or equal to 63 bytes (6 bits).
 * |01pppppp|qqqqqqqq| - 2 bytes
 *      String value with length less than or equal to 16383 bytes (14 bits).
 * |10______|qqqqqqqq|rrrrrrrr|ssssssss|tttttttt| - 5 bytes
 *      String value with length greater than or equal to 16384 bytes.
 * |11000000| - 1 byte
 *      Integer encoded as int16_t (2 bytes).
 * |11010000| - 1 byte
 *      Integer encoded as int32_t (4 bytes).
 * |11100000| - 1 byte
 *      Integer encoded as int64_t (8 bytes).
 * |11110000| - 1 byte
 *      Integer encoded as 24 bit signed (3 bytes).
 * |11111110| - 1 byte
 *      Integer encoded as 8 bit signed (1 byte).
 * |1111xxxx| - (with xxxx between 0000 and 1101) immediate 4 bit integer.
 *      Unsigned integer from 0 to 12. The encoded value is actually from
 *      1 to 13 because 0000 and 1111 can not be used, so 1 should be
 *      subtracted from the encoded 4 bit value to obtain the right value.
 * |11111111| - End of ziplist.
 *
 * All the integers are represented in little endian byte order.
 *
 * ----------------------------------------------------------------------------
 *
 * Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>
 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <limits.h>
#include <assert.h>
#include "../lib/zmalloc.h"
#include "../lib/util.h"
#include "../lib/ziplist.h"


#define ZIP_END 255
#define ZIP_BIGLEN 254

/* Different encoding/length possibilities */
#define ZIP_STR_MASK 0xc0
#define ZIP_INT_MASK 0x30
#define ZIP_STR_06B (0 << 6)
#define ZIP_STR_14B (1 << 6)
#define ZIP_STR_32B (2 << 6)
#define ZIP_INT_16B (0xc0 | 0<<4)
#define ZIP_INT_32B (0xc0 | 1<<4)
#define ZIP_INT_64B (0xc0 | 2<<4)
#define ZIP_INT_24B (0xc0 | 3<<4)
#define ZIP_INT_8B 0xfe
/* 4 bit integer immediate encoding */
#define ZIP_INT_IMM_MASK 0x0f
#define ZIP_INT_IMM_MIN 0xf1    /* 11110001 */
#define ZIP_INT_IMM_MAX 0xfd    /* 11111101 */
#define ZIP_INT_IMM_VAL(v) (v & ZIP_INT_IMM_MASK)

#define INT24_MAX 0x7fffff
#define INT24_MIN (-INT24_MAX - 1)

/* Macro to determine type */
#define ZIP_IS_STR(enc) (((enc) & ZIP_STR_MASK) < ZIP_STR_MASK)
#define intrev16ifbe(v) (v)
#define intrev32ifbe(v) (v)

/* Utility macros */
#define ZIPLIST_BYTES(zl)       (*((uint32_t*)(zl)))
#define ZIPLIST_TAIL_OFFSET(zl) (*((uint32_t*)((zl)+sizeof(uint32_t))))
#define ZIPLIST_LENGTH(zl)      (*((uint16_t*)((zl)+sizeof(uint32_t)*2)))
#define ZIPLIST_HEADER_SIZE     (sizeof(uint32_t)*2+sizeof(uint16_t))
#define ZIPLIST_END_SIZE        (sizeof(uint8_t))
#define ZIPLIST_ENTRY_HEAD(zl)  ((zl)+ZIPLIST_HEADER_SIZE)
#define ZIPLIST_ENTRY_TAIL(zl)  ((zl)+intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl)))
#define ZIPLIST_ENTRY_END(zl)   ((zl)+intrev32ifbe(ZIPLIST_BYTES(zl))-1)

/* We know a positive increment can only be 1 because entries can only be
 * pushed one at a time. */
#define ZIPLIST_INCR_LENGTH(zl,incr) { \
    if (ZIPLIST_LENGTH(zl) < UINT16_MAX) \
        ZIPLIST_LENGTH(zl) = intrev16ifbe(intrev16ifbe(ZIPLIST_LENGTH(zl))+incr); \
}

typedef struct zlentry
{
    unsigned int prevrawlensize, prevrawlen;
    unsigned int lensize, len;
    unsigned int headersize;
    unsigned char encoding;
    unsigned char *p;
} zlentry;

#define ZIPLIST_ENTRY_ZERO(zle) { \
    (zle)->prevrawlensize = (zle)->prevrawlen = 0; \
    (zle)->lensize = (zle)->len = (zle)->headersize = 0; \
    (zle)->encoding = 0; \
    (zle)->p = NULL; \
}

/* Extract the encoding from the byte pointed by 'ptr' and set it into
 * 'encoding'. */
#define ZIP_ENTRY_ENCODING(ptr, encoding) do {  \
    (encoding) = (ptr[0]); \
    if ((encoding) < ZIP_STR_MASK) (encoding) &= ZIP_STR_MASK; \
} while(0)

void ziplistRepr ( unsigned char *zl );

/* Return bytes needed to store integer encoded by 'encoding' */
static unsigned int zipIntSize ( unsigned char encoding )
{
    switch ( encoding )
    {
        case ZIP_INT_8B: return 1;
        case ZIP_INT_16B: return 2;
        case ZIP_INT_24B: return 3;
        case ZIP_INT_32B: return 4;
        case ZIP_INT_64B: return 8;
        default: return 0; /* 4 bit immediate */
    }
    assert (NULL);
    return 0;
}

/* Encode the length 'rawlen' writing it in 'p'. If p is NULL it just returns
 * the amount of bytes required to encode such a length. */
static unsigned int zipEncodeLength ( unsigned char *p, unsigned char encoding, unsigned int rawlen )
{
    unsigned char len = 1, buf[5];

    if ( ZIP_IS_STR (encoding) )
    {
        /* Although encoding is given it may not be set for strings,
         * so we determine it here using the raw length. */
        if ( rawlen <= 0x3f )
        {
            if ( ! p ) return len;
            buf[0] = ZIP_STR_06B | rawlen;
        }
        else if ( rawlen <= 0x3fff )
        {
            len += 1;
            if ( ! p ) return len;
            buf[0] = ZIP_STR_14B | ( ( rawlen >> 8 ) & 0x3f );
            buf[1] = rawlen & 0xff;
        }
        else
        {
            len += 4;
            if ( ! p ) return len;
            buf[0] = ZIP_STR_32B;
            buf[1] = ( rawlen >> 24 ) & 0xff;
            buf[2] = ( rawlen >> 16 ) & 0xff;
            buf[3] = ( rawlen >> 8 ) & 0xff;
            buf[4] = rawlen & 0xff;
        }
    }
    else
    {
        /* Implies integer encoding, so length is always 1. */
        if ( ! p ) return len;
        buf[0] = encoding;
    }

    /* Store this length at p */
    memcpy (p, buf, len);
    return len;
}

/* Decode the length encoded in 'ptr'. The 'encoding' variable will hold the
 * entries encoding, the 'lensize' variable will hold the number of bytes
 * required to encode the entries length, and the 'len' variable will hold the
 * entries length. */
#define ZIP_DECODE_LENGTH(ptr, encoding, lensize, len) do {                    \
    ZIP_ENTRY_ENCODING((ptr), (encoding));                                     \
    if ((encoding) < ZIP_STR_MASK) {                                           \
        if ((encoding) == ZIP_STR_06B) {                                       \
            (lensize) = 1;                                                     \
            (len) = (ptr)[0] & 0x3f;                                           \
        } else if ((encoding) == ZIP_STR_14B) {                                \
            (lensize) = 2;                                                     \
            (len) = (((ptr)[0] & 0x3f) << 8) | (ptr)[1];                       \
        } else if (encoding == ZIP_STR_32B) {                                  \
            (lensize) = 5;                                                     \
            (len) = ((ptr)[1] << 24) |                                         \
                    ((ptr)[2] << 16) |                                         \
                    ((ptr)[3] <<  8) |                                         \
                    ((ptr)[4]);                                                \
        } else {                                                               \
            assert(NULL);                                                      \
        }                                                                      \
    } else {                                                                   \
        (lensize) = 1;                                                         \
        (len) = zipIntSize(encoding);                                          \
    }                                                                          \
} while(0);

/* Encode the length of the previous entry and write it to "p". Return the
 * number of bytes needed to encode this length if "p" is NULL. */
static unsigned int zipPrevEncodeLength ( unsigned char *p, unsigned int len )
{
    if ( p == NULL )
    {
        return (len < ZIP_BIGLEN ) ? 1 : sizeof (len ) + 1;
    }
    else
    {
        if ( len < ZIP_BIGLEN )
        {
            p[0] = len;
            return 1;
        }
        else
        {
            p[0] = ZIP_BIGLEN;
            memcpy (p + 1, &len, sizeof (len ));
            return 1 + sizeof (len );
        }
    }
}

/* Encode the length of the previous entry and write it to "p". This only
 * uses the larger encoding (required in __ziplistCascadeUpdate). */
static void zipPrevEncodeLengthForceLarge ( unsigned char *p, unsigned int len )
{
    if ( p == NULL ) return;
    p[0] = ZIP_BIGLEN;
    memcpy (p + 1, &len, sizeof (len ));
}

/* Decode the number of bytes required to store the length of the previous
 * element, from the perspective of the entry pointed to by 'ptr'. */
#define ZIP_DECODE_PREVLENSIZE(ptr, prevlensize) do {                          \
    if ((ptr)[0] < ZIP_BIGLEN) {                                               \
        (prevlensize) = 1;                                                     \
    } else {                                                                   \
        (prevlensize) = 5;                                                     \
    }                                                                          \
} while(0);

/* Decode the length of the previous element, from the perspective of the entry
 * pointed to by 'ptr'. */
#define ZIP_DECODE_PREVLEN(ptr, prevlensize, prevlen) do {                     \
    ZIP_DECODE_PREVLENSIZE(ptr, prevlensize);                                  \
    if ((prevlensize) == 1) {                                                  \
        (prevlen) = (ptr)[0];                                                  \
    } else if ((prevlensize) == 5) {                                           \
        assert(sizeof((prevlensize)) == 4);                                    \
        memcpy(&(prevlen), ((char*)(ptr)) + 1, 4);                             \
    }                                                                          \
} while(0);

/* Return the difference in number of bytes needed to store the length of the
 * previous element 'len', in the entry pointed to by 'p'. */
static int zipPrevLenByteDiff ( unsigned char *p, unsigned int len )
{
    unsigned int prevlensize;
    ZIP_DECODE_PREVLENSIZE (p, prevlensize);
    return zipPrevEncodeLength (NULL, len) - prevlensize;
}

/* Return the total number of bytes used by the entry pointed to by 'p'. */
static unsigned int zipRawEntryLength ( unsigned char *p )
{
    unsigned int prevlensize, encoding, lensize, len;
    ZIP_DECODE_PREVLENSIZE (p, prevlensize);
    ZIP_DECODE_LENGTH (p + prevlensize, encoding, lensize, len);
    return prevlensize + lensize + len;
}

/* Check if string pointed to by 'entry' can be encoded as an integer.
 * Stores the integer value in 'v' and its encoding in 'encoding'. */
static int zipTryEncoding ( unsigned char *entry, unsigned int entrylen, long long *v, unsigned char *encoding )
{
    long long value;

    if ( entrylen >= 32 || entrylen == 0 ) return 0;
    if ( string2ll (( char* ) entry, entrylen, &value) )
    {
        /* Great, the string can be encoded. Check what's the smallest
         * of our encoding types that can hold this value. */
        if ( value >= 0 && value <= 12 )
        {
            *encoding = ZIP_INT_IMM_MIN + value;
        }
        else if ( value >= INT8_MIN && value <= INT8_MAX )
        {
            *encoding = ZIP_INT_8B;
        }
        else if ( value >= INT16_MIN && value <= INT16_MAX )
        {
            *encoding = ZIP_INT_16B;
        }
        else if ( value >= INT24_MIN && value <= INT24_MAX )
        {
            *encoding = ZIP_INT_24B;
        }
        else if ( value >= INT32_MIN && value <= INT32_MAX )
        {
            *encoding = ZIP_INT_32B;
        }
        else
        {
            *encoding = ZIP_INT_64B;
        }
        *v = value;
        return 1;
    }
    return 0;
}

/* Store integer 'value' at 'p', encoded as 'encoding' */
static void zipSaveInteger ( unsigned char *p, int64_t value, unsigned char encoding )
{
    int16_t i16;
    int32_t i32;
    int64_t i64;
    if ( encoding == ZIP_INT_8B )
    {
        ( ( int8_t* ) p )[0] = ( int8_t ) value;
    }
    else if ( encoding == ZIP_INT_16B )
    {
        i16 = value;
        memcpy (p, &i16, sizeof (i16 ));
    }
    else if ( encoding == ZIP_INT_24B )
    {
        i32 = value << 8;
        memcpy (p, ( ( uint8_t* ) & i32 ) + 1, sizeof (i32 ) - sizeof (uint8_t ));
    }
    else if ( encoding == ZIP_INT_32B )
    {
        i32 = value;
        memcpy (p, &i32, sizeof (i32 ));
    }
    else if ( encoding == ZIP_INT_64B )
    {
        i64 = value;
        memcpy (p, &i64, sizeof (i64 ));
    }
    else if ( encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX )
    {
        /* Nothing to do, the value is stored in the encoding itself. */
    }
    else
    {
        assert (NULL);
    }
}

/* Read integer encoded as 'encoding' from 'p' */
static int64_t zipLoadInteger ( unsigned char *p, unsigned char encoding )
{
    int16_t i16;
    int32_t i32;
    int64_t i64, ret = 0;
    if ( encoding == ZIP_INT_8B )
    {
        ret = ( ( int8_t* ) p )[0];
    }
    else if ( encoding == ZIP_INT_16B )
    {
        memcpy (&i16, p, sizeof (i16 ));
        ret = i16;
    }
    else if ( encoding == ZIP_INT_32B )
    {
        memcpy (&i32, p, sizeof (i32 ));
        ret = i32;
    }
    else if ( encoding == ZIP_INT_24B )
    {
        i32 = 0;
        memcpy (( ( uint8_t* ) & i32 ) + 1, p, sizeof (i32 ) - sizeof (uint8_t ));
        ret = i32 >> 8;
    }
    else if ( encoding == ZIP_INT_64B )
    {
        memcpy (&i64, p, sizeof (i64 ));
        ret = i64;
    }
    else if ( encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX )
    {
        ret = ( encoding & ZIP_INT_IMM_MASK ) - 1;
    }
    else
    {
        assert (NULL);
    }
    return ret;
}

/* Return a struct with all information about an entry. */
static void zipEntry ( unsigned char *p, zlentry *e )
{

    ZIP_DECODE_PREVLEN (p, e->prevrawlensize, e->prevrawlen);
    ZIP_DECODE_LENGTH (p + e->prevrawlensize, e->encoding, e->lensize, e->len);
    e->headersize = e->prevrawlensize + e->lensize;
    e->p = p;
}

/* Create a new empty ziplist. */
unsigned char *ziplistNew ( void )
{
    unsigned int bytes = ZIPLIST_HEADER_SIZE + 1;
    unsigned char *zl = zmalloc (bytes);
    ZIPLIST_BYTES (zl) = intrev32ifbe (bytes);
    ZIPLIST_TAIL_OFFSET (zl) = intrev32ifbe (ZIPLIST_HEADER_SIZE);
    ZIPLIST_LENGTH (zl) = 0;
    zl[bytes - 1] = ZIP_END;
    return zl;
}

/* Resize the ziplist. */
static unsigned char *ziplistResize ( unsigned char *zl, unsigned int len )
{
    zl = zrealloc (zl, len);
    ZIPLIST_BYTES (zl) = intrev32ifbe (len);
    zl[len - 1] = ZIP_END;
    return zl;
}

/* When an entry is inserted, we need to set the prevlen field of the next
 * entry to equal the length of the inserted entry. It can occur that this
 * length cannot be encoded in 1 byte and the next entry needs to be grow
 * a bit larger to hold the 5-byte encoded prevlen. This can be done for free,
 * because this only happens when an entry is already being inserted (which
 * causes a realloc and memmove). However, encoding the prevlen may require
 * that this entry is grown as well. This effect may cascade throughout
 * the ziplist when there are consecutive entries with a size close to
 * ZIP_BIGLEN, so we need to check that the prevlen can be encoded in every
 * consecutive entry.
 *
 * Note that this effect can also happen in reverse, where the bytes required
 * to encode the prevlen field can shrink. This effect is deliberately ignored,
 * because it can cause a "flapping" effect where a chain prevlen fields is
 * first grown and then shrunk again after consecutive inserts. Rather, the
 * field is allowed to stay larger than necessary, because a large prevlen
 * field implies the ziplist is holding large entries anyway.
 *
 * The pointer "p" points to the first entry that does NOT need to be
 * updated, i.e. consecutive fields MAY need an update. */
static unsigned char *__ziplistCascadeUpdate ( unsigned char *zl, unsigned char *p )
{
    size_t curlen = intrev32ifbe (ZIPLIST_BYTES (zl)), rawlen, rawlensize;
    size_t offset, noffset, extra;
    unsigned char *np;
    zlentry cur, next;

    while ( p[0] != ZIP_END )
    {
        zipEntry (p, &cur);
        rawlen = cur.headersize + cur.len;
        rawlensize = zipPrevEncodeLength (NULL, rawlen);

        /* Abort if there is no next entry. */
        if ( p[rawlen] == ZIP_END ) break;
        zipEntry (p + rawlen, &next);

        /* Abort when "prevlen" has not changed. */
        if ( next.prevrawlen == rawlen ) break;

        if ( next.prevrawlensize < rawlensize )
        {
            /* The "prevlen" field of "next" needs more bytes to hold
             * the raw length of "cur". */
            offset = p - zl;
            extra = rawlensize - next.prevrawlensize;
            zl = ziplistResize (zl, curlen + extra);
            p = zl + offset;

            /* Current pointer and offset for next element. */
            np = p + rawlen;
            noffset = np - zl;

            /* Update tail offset when next element is not the tail element. */
            if ( ( zl + intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)) ) != np )
            {
                ZIPLIST_TAIL_OFFSET (zl) =
                    intrev32ifbe (intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)) + extra);
            }

            /* Move the tail to the back. */
            memmove (np + rawlensize,
                     np + next.prevrawlensize,
                     curlen - noffset - next.prevrawlensize - 1);
            zipPrevEncodeLength (np, rawlen);

            /* Advance the cursor */
            p += rawlen;
            curlen += extra;
        }
        else
        {
            if ( next.prevrawlensize > rawlensize )
            {
                /* This would result in shrinking, which we want to avoid.
                 * So, set "rawlen" in the available bytes. */
                zipPrevEncodeLengthForceLarge (p + rawlen, rawlen);
            }
            else
            {
                zipPrevEncodeLength (p + rawlen, rawlen);
            }

            /* Stop here, as the raw length of "next" has not changed. */
            break;
        }
    }
    return zl;
}

/* Delete "num" entries, starting at "p". Returns pointer to the ziplist. */
static unsigned char *__ziplistDelete ( unsigned char *zl, unsigned char *p, unsigned int num )
{
    unsigned int i, totlen, deleted = 0;
    size_t offset;
    int nextdiff = 0;
    zlentry first, tail;

    zipEntry (p, &first);
    for ( i = 0; p[0] != ZIP_END && i < num; i ++ )
    {
        p += zipRawEntryLength (p);
        deleted ++;
    }

    totlen = p - first.p;
    if ( totlen > 0 )
    {
        if ( p[0] != ZIP_END )
        {
            /* Storing `prevrawlen` in this entry may increase or decrease the
             * number of bytes required compare to the current `prevrawlen`.
             * There always is room to store this, because it was previously
             * stored by an entry that is now being deleted. */
            nextdiff = zipPrevLenByteDiff (p, first.prevrawlen);
            p -= nextdiff;
            zipPrevEncodeLength (p, first.prevrawlen);

            /* Update offset for tail */
            ZIPLIST_TAIL_OFFSET (zl) =
                intrev32ifbe (intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)) - totlen);

            /* When the tail contains more than one entry, we need to take
             * "nextdiff" in account as well. Otherwise, a change in the
             * size of prevlen doesn't have an effect on the *tail* offset. */
            zipEntry (p, &tail);
            if ( p[tail.headersize + tail.len] != ZIP_END )
            {
                ZIPLIST_TAIL_OFFSET (zl) =
                    intrev32ifbe (intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)) + nextdiff);
            }

            /* Move tail to the front of the ziplist */
            memmove (first.p, p,
                     intrev32ifbe (ZIPLIST_BYTES (zl))-( p - zl ) - 1);
        }
        else
        {
            /* The entire tail was deleted. No need to move memory. */
            ZIPLIST_TAIL_OFFSET (zl) =
                intrev32ifbe (( first.p - zl ) - first.prevrawlen);
        }

        /* Resize and update length */
        offset = first.p - zl;
        zl = ziplistResize (zl, intrev32ifbe (ZIPLIST_BYTES (zl)) - totlen + nextdiff);
        ZIPLIST_INCR_LENGTH (zl, - deleted);
        p = zl + offset;

        /* When nextdiff != 0, the raw length of the next entry has changed, so
         * we need to cascade the update throughout the ziplist */
        if ( nextdiff != 0 )
            zl = __ziplistCascadeUpdate (zl, p);
    }
    return zl;
}

/* Insert item at "p". */
static unsigned char *__ziplistInsert ( unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen )
{
    size_t curlen = intrev32ifbe (ZIPLIST_BYTES (zl)), reqlen;
    unsigned int prevlensize, prevlen = 0;
    size_t offset;
    int nextdiff = 0;
    unsigned char encoding = 0;
    long long value = 123456789; /* initialized to avoid warning. Using a value
                                    that is easy to see if for some reason
                                    we use it uninitialized. */
    zlentry tail;

    /* Find out prevlen for the entry that is inserted. */
    if ( p[0] != ZIP_END )
    {
        ZIP_DECODE_PREVLEN (p, prevlensize, prevlen);
    }
    else
    {
        unsigned char *ptail = ZIPLIST_ENTRY_TAIL (zl);
        if ( ptail[0] != ZIP_END )
        {
            prevlen = zipRawEntryLength (ptail);
        }
    }

    /* See if the entry can be encoded */
    if ( zipTryEncoding (s, slen, &value, &encoding) )
    {
        /* 'encoding' is set to the appropriate integer encoding */
        reqlen = zipIntSize (encoding);
    }
    else
    {
        /* 'encoding' is untouched, however zipEncodeLength will use the
         * string length to figure out how to encode it. */
        reqlen = slen;
    }
    /* We need space for both the length of the previous entry and
     * the length of the payload. */
    reqlen += zipPrevEncodeLength (NULL, prevlen);
    reqlen += zipEncodeLength (NULL, encoding, slen);

    /* When the insert position is not equal to the tail, we need to
     * make sure that the next entry can hold this entry's length in
     * its prevlen field. */
    nextdiff = ( p[0] != ZIP_END ) ? zipPrevLenByteDiff (p, reqlen) : 0;

    /* Store offset because a realloc may change the address of zl. */
    offset = p - zl;
    zl = ziplistResize (zl, curlen + reqlen + nextdiff);
    p = zl + offset;

    /* Apply memory move when necessary and update tail offset. */
    if ( p[0] != ZIP_END )
    {
        /* Subtract one because of the ZIP_END bytes */
        memmove (p + reqlen, p - nextdiff, curlen - offset - 1 + nextdiff);

        /* Encode this entry's raw length in the next entry. */
        zipPrevEncodeLength (p + reqlen, reqlen);

        /* Update offset for tail */
        ZIPLIST_TAIL_OFFSET (zl) =
            intrev32ifbe (intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)) + reqlen);

        /* When the tail contains more than one entry, we need to take
         * "nextdiff" in account as well. Otherwise, a change in the
         * size of prevlen doesn't have an effect on the *tail* offset. */
        zipEntry (p + reqlen, &tail);
        if ( p[reqlen + tail.headersize + tail.len] != ZIP_END )
        {
            ZIPLIST_TAIL_OFFSET (zl) =
                intrev32ifbe (intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)) + nextdiff);
        }
    }
    else
    {
        /* This element will be the new tail. */
        ZIPLIST_TAIL_OFFSET (zl) = intrev32ifbe (p - zl);
    }

    /* When nextdiff != 0, the raw length of the next entry has changed, so
     * we need to cascade the update throughout the ziplist */
    if ( nextdiff != 0 )
    {
        offset = p - zl;
        zl = __ziplistCascadeUpdate (zl, p + reqlen);
        p = zl + offset;
    }

    /* Write the entry */
    p += zipPrevEncodeLength (p, prevlen);
    p += zipEncodeLength (p, encoding, slen);
    if ( ZIP_IS_STR (encoding) )
    {
        memcpy (p, s, slen);
    }
    else
    {
        zipSaveInteger (p, value, encoding);
    }
    ZIPLIST_INCR_LENGTH (zl, 1);
    return zl;
}

/* Merge ziplists 'first' and 'second' by appending 'second' to 'first'.
 *
 * NOTE: The larger ziplist is reallocated to contain the new merged ziplist.
 * Either 'first' or 'second' can be used for the result.  The parameter not
 * used will be free'd and set to NULL.
 *
 * After calling this function, the input parameters are no longer valid since
 * they are changed and free'd in-place.
 *
 * The result ziplist is the contents of 'first' followed by 'second'.
 *
 * On failure: returns NULL if the merge is impossible.
 * On success: returns the merged ziplist (which is expanded version of either
 * 'first' or 'second', also frees the other unused input ziplist, and sets the
 * input ziplist argument equal to newly reallocated ziplist return value. */
unsigned char *ziplistMerge ( unsigned char **first, unsigned char **second )
{
    /* If any params are null, we can't merge, so NULL. */
    if ( first == NULL || * first == NULL || second == NULL || * second == NULL )
        return NULL;

    /* Can't merge same list into itself. */
    if ( *first == * second )
        return NULL;

    size_t first_bytes = intrev32ifbe (ZIPLIST_BYTES (*first));
    size_t first_len = intrev16ifbe (ZIPLIST_LENGTH (*first));

    size_t second_bytes = intrev32ifbe (ZIPLIST_BYTES (*second));
    size_t second_len = intrev16ifbe (ZIPLIST_LENGTH (*second));

    int append;
    unsigned char *source, *target;
    size_t target_bytes, source_bytes;
    /* Pick the largest ziplist so we can resize easily in-place.
     * We must also track if we are now appending or prepending to
     * the target ziplist. */
    if ( first_len >= second_len )
    {
        /* retain first, append second to first. */
        target = * first;
        target_bytes = first_bytes;
        source = * second;
        source_bytes = second_bytes;
        append = 1;
    }
    else
    {
        /* else, retain second, prepend first to second. */
        target = * second;
        target_bytes = second_bytes;
        source = * first;
        source_bytes = first_bytes;
        append = 0;
    }

    /* Calculate final bytes (subtract one pair of metadata) */
    size_t zlbytes = first_bytes + second_bytes -
        ZIPLIST_HEADER_SIZE - ZIPLIST_END_SIZE;
    size_t zllength = first_len + second_len;

    /* Combined zl length should be limited within UINT16_MAX */
    zllength = zllength < UINT16_MAX ? zllength : UINT16_MAX;

    /* Save offset positions before we start ripping memory apart. */
    size_t first_offset = intrev32ifbe (ZIPLIST_TAIL_OFFSET (*first));
    size_t second_offset = intrev32ifbe (ZIPLIST_TAIL_OFFSET (*second));

    /* Extend target to new zlbytes then append or prepend source. */
    target = zrealloc (target, zlbytes);
    if ( append )
    {
        /* append == appending to target */
        /* Copy source after target (copying over original [END]):
         *   [TARGET - END, SOURCE - HEADER] */
        memcpy (target + target_bytes - ZIPLIST_END_SIZE,
                source + ZIPLIST_HEADER_SIZE,
                source_bytes - ZIPLIST_HEADER_SIZE);
    }
    else
    {
        /* !append == prepending to target */
        /* Move target *contents* exactly size of (source - [END]),
         * then copy source into vacataed space (source - [END]):
         *   [SOURCE - END, TARGET - HEADER] */
        memmove (target + source_bytes - ZIPLIST_END_SIZE,
                 target + ZIPLIST_HEADER_SIZE,
                 target_bytes - ZIPLIST_HEADER_SIZE);
        memcpy (target, source, source_bytes - ZIPLIST_END_SIZE);
    }

    /* Update header metadata. */
    ZIPLIST_BYTES (target) = intrev32ifbe (zlbytes);
    ZIPLIST_LENGTH (target) = intrev16ifbe (zllength);
    /* New tail offset is:
     *   + N bytes of first ziplist
     *   - 1 byte for [END] of first ziplist
     *   + M bytes for the offset of the original tail of the second ziplist
     *   - J bytes for HEADER because second_offset keeps no header. */
    ZIPLIST_TAIL_OFFSET (target) = intrev32ifbe (
                                                 ( first_bytes - ZIPLIST_END_SIZE ) +
                                                 ( second_offset - ZIPLIST_HEADER_SIZE ));

    /* __ziplistCascadeUpdate just fixes the prev length values until it finds a
     * correct prev length value (then it assumes the rest of the list is okay).
     * We tell CascadeUpdate to start at the first ziplist's tail element to fix
     * the merge seam. */
    target = __ziplistCascadeUpdate (target, target + first_offset);

    /* Now free and NULL out what we didn't realloc */
    if ( append )
    {
        zfree (*second);
        *second = NULL;
        *first = target;
    }
    else
    {
        zfree (*first);
        *first = NULL;
        *second = target;
    }
    return target;
}

unsigned char *ziplistPush ( unsigned char *zl, unsigned char *s, unsigned int slen, int where )
{
    unsigned char *p;
    p = ( where == ZIPLIST_HEAD ) ? ZIPLIST_ENTRY_HEAD (zl) : ZIPLIST_ENTRY_END (zl);
    return __ziplistInsert (zl, p, s, slen);
}

/* Returns an offset to use for iterating with ziplistNext. When the given
 * index is negative, the list is traversed back to front. When the list
 * doesn't contain an element at the provided index, NULL is returned. */
unsigned char *ziplistIndex ( unsigned char *zl, int index )
{
    unsigned char *p;
    unsigned int prevlensize, prevlen = 0;
    if ( index < 0 )
    {
        index = ( - index ) - 1;
        p = ZIPLIST_ENTRY_TAIL (zl);
        if ( p[0] != ZIP_END )
        {
            ZIP_DECODE_PREVLEN (p, prevlensize, prevlen);
            while ( prevlen > 0 && index -- )
            {
                p -= prevlen;
                ZIP_DECODE_PREVLEN (p, prevlensize, prevlen);
            }
        }
    }
    else
    {
        p = ZIPLIST_ENTRY_HEAD (zl);
        while ( p[0] != ZIP_END && index -- )
        {
            p += zipRawEntryLength (p);
        }
    }
    return (p[0] == ZIP_END || index > 0 ) ? NULL : p;
}

/* Return pointer to next entry in ziplist.
 *
 * zl is the pointer to the ziplist
 * p is the pointer to the current element
 *
 * The element after 'p' is returned, otherwise NULL if we are at the end. */
unsigned char *ziplistNext ( unsigned char *zl, unsigned char *p )
{
    ( ( void ) zl );

    /* "p" could be equal to ZIP_END, caused by ziplistDelete,
     * and we should return NULL. Otherwise, we should return NULL
     * when the *next* element is ZIP_END (there is no next entry). */
    if ( p[0] == ZIP_END )
    {
        return NULL;
    }

    p += zipRawEntryLength (p);
    if ( p[0] == ZIP_END )
    {
        return NULL;
    }

    return p;
}

/* Return pointer to previous entry in ziplist. */
unsigned char *ziplistPrev ( unsigned char *zl, unsigned char *p )
{
    unsigned int prevlensize, prevlen = 0;

    /* Iterating backwards from ZIP_END should return the tail. When "p" is
     * equal to the first element of the list, we're already at the head,
     * and should return NULL. */
    if ( p[0] == ZIP_END )
    {
        p = ZIPLIST_ENTRY_TAIL (zl);
        return (p[0] == ZIP_END ) ? NULL : p;
    }
    else if ( p == ZIPLIST_ENTRY_HEAD (zl) )
    {
        return NULL;
    }
    else
    {
        ZIP_DECODE_PREVLEN (p, prevlensize, prevlen);
        assert (prevlen > 0);
        return p - prevlen;
    }
}

/* Get entry pointed to by 'p' and store in either '*sstr' or 'sval' depending
 * on the encoding of the entry. '*sstr' is always set to NULL to be able
 * to find out whether the string pointer or the integer value was set.
 * Return 0 if 'p' points to the end of the ziplist, 1 otherwise. */
unsigned int ziplistGet ( unsigned char *p, unsigned char **sstr, unsigned int *slen, long long *sval )
{
    zlentry entry;
    if ( p == NULL || p[0] == ZIP_END ) return 0;
    if ( sstr ) *sstr = NULL;

    zipEntry (p, &entry);
    if ( ZIP_IS_STR (entry.encoding) )
    {
        if ( sstr )
        {
            *slen = entry.len;
            *sstr = p + entry.headersize;
        }
    }
    else
    {
        if ( sval )
        {
            *sval = zipLoadInteger (p + entry.headersize, entry.encoding);
        }
    }
    return 1;
}

/* Insert an entry at "p". */
unsigned char *ziplistInsert ( unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen )
{
    return __ziplistInsert (zl, p, s, slen);
}

/* Delete a single entry from the ziplist, pointed to by *p.
 * Also update *p in place, to be able to iterate over the
 * ziplist, while deleting entries. */
unsigned char *ziplistDelete ( unsigned char *zl, unsigned char **p )
{
    size_t offset = * p - zl;
    zl = __ziplistDelete (zl, *p, 1);

    /* Store pointer to current element in p, because ziplistDelete will
     * do a realloc which might result in a different "zl"-pointer.
     * When the delete direction is back to front, we might delete the last
     * entry and end up with "p" pointing to ZIP_END, so check this. */
    *p = zl + offset;
    return zl;
}

/* Delete a range of entries from the ziplist. */
unsigned char *ziplistDeleteRange ( unsigned char *zl, int index, unsigned int num )
{
    unsigned char *p = ziplistIndex (zl, index);
    return (p == NULL ) ? zl : __ziplistDelete (zl, p, num);
}

/* Compare entry pointer to by 'p' with 'sstr' of length 'slen'. */

/* Return 1 if equal. */
unsigned int ziplistCompare ( unsigned char *p, unsigned char *sstr, unsigned int slen )
{
    zlentry entry;
    unsigned char sencoding;
    long long zval, sval;
    if ( p[0] == ZIP_END ) return 0;

    zipEntry (p, &entry);
    if ( ZIP_IS_STR (entry.encoding) )
    {
        /* Raw compare */
        if ( entry.len == slen )
        {
            return memcmp (p + entry.headersize, sstr, slen) == 0;
        }
        else
        {
            return 0;
        }
    }
    else
    {
        /* Try to compare encoded values. Don't compare encoding because
         * different implementations may encoded integers differently. */
        if ( zipTryEncoding (sstr, slen, &sval, &sencoding) )
        {
            zval = zipLoadInteger (p + entry.headersize, entry.encoding);
            return zval == sval;
        }
    }
    return 0;
}

/* Find pointer to the entry equal to the specified entry. Skip 'skip' entries
 * between every comparison. Returns NULL when the field could not be found. */
unsigned char *ziplistFind ( unsigned char *p, unsigned char *vstr, unsigned int vlen, unsigned int skip )
{
    int skipcnt = 0;
    unsigned char vencoding = 0;
    long long vll = 0;

    while ( p[0] != ZIP_END )
    {
        unsigned int prevlensize, encoding, lensize, len;
        unsigned char *q;

        ZIP_DECODE_PREVLENSIZE (p, prevlensize);
        ZIP_DECODE_LENGTH (p + prevlensize, encoding, lensize, len);
        q = p + prevlensize + lensize;

        if ( skipcnt == 0 )
        {
            /* Compare current entry with specified entry */
            if ( ZIP_IS_STR (encoding) )
            {
                if ( len == vlen && memcmp (q, vstr, vlen) == 0 )
                {
                    return p;
                }
            }
            else
            {
                /* Find out if the searched field can be encoded. Note that
                 * we do it only the first time, once done vencoding is set
                 * to non-zero and vll is set to the integer value. */
                if ( vencoding == 0 )
                {
                    if ( ! zipTryEncoding (vstr, vlen, &vll, &vencoding) )
                    {
                        /* If the entry can't be encoded we set it to
                         * UCHAR_MAX so that we don't retry again the next
                         * time. */
                        vencoding = UCHAR_MAX;
                    }
                    /* Must be non-zero by now */
                    assert (vencoding);
                }

                /* Compare current entry with specified entry, do it only
                 * if vencoding != UCHAR_MAX because if there is no encoding
                 * possible for the field it can't be a valid integer. */
                if ( vencoding != UCHAR_MAX )
                {
                    long long ll = zipLoadInteger (q, encoding);
                    if ( ll == vll )
                    {
                        return p;
                    }
                }
            }

            /* Reset skip count */
            skipcnt = skip;
        }
        else
        {
            /* Skip entry */
            skipcnt --;
        }

        /* Move to next entry */
        p = q + len;
    }

    return NULL;
}

/* Return length of ziplist. */
unsigned int ziplistLen ( unsigned char *zl )
{
    unsigned int len = 0;
    if ( intrev16ifbe (ZIPLIST_LENGTH (zl)) < UINT16_MAX )
    {
        len = intrev16ifbe (ZIPLIST_LENGTH (zl));
    }
    else
    {
        unsigned char *p = zl + ZIPLIST_HEADER_SIZE;
        while ( *p != ZIP_END )
        {
            p += zipRawEntryLength (p);
            len ++;
        }

        /* Re-store length if small enough */
        if ( len < UINT16_MAX ) ZIPLIST_LENGTH (zl) = intrev16ifbe (len);
    }
    return len;
}

/* Return ziplist blob size in bytes. */
size_t ziplistBlobLen ( unsigned char *zl )
{
    return intrev32ifbe (ZIPLIST_BYTES (zl));
}

void ziplistRepr ( unsigned char *zl )
{
    unsigned char *p;
    int index = 0;
    zlentry entry;

    printf (
            "{total bytes %d} "
            "{length %u}\n"
            "{tail offset %u}\n",
            intrev32ifbe (ZIPLIST_BYTES (zl)),
            intrev16ifbe (ZIPLIST_LENGTH (zl)),
            intrev32ifbe (ZIPLIST_TAIL_OFFSET (zl)));
    p = ZIPLIST_ENTRY_HEAD (zl);
    while ( *p != ZIP_END )
    {
        zipEntry (p, &entry);
        printf (
                "{"
                "addr 0x%08lx, "
                "index %2d, "
                "offset %5ld, "
                "rl: %5u, "
                "hs %2u, "
                "pl: %5u, "
                "pls: %2u, "
                "payload %5u"
                "} ",
                ( long unsigned ) p,
                index,
                ( unsigned long ) ( p - zl ),
                entry.headersize + entry.len,
                entry.headersize,
                entry.prevrawlen,
                entry.prevrawlensize,
                entry.len);
        p += entry.headersize;
        if ( ZIP_IS_STR (entry.encoding) )
        {
            if ( entry.len > 40 )
            {
                if ( fwrite (p, 40, 1, stdout) == 0 ) perror ("fwrite");
                printf ("...");
            }
            else
            {
                if ( entry.len &&
                     fwrite (p, entry.len, 1, stdout) == 0 ) perror ("fwrite");
            }
        }
        else
        {
            printf ("%lld", ( long long ) zipLoadInteger (p, entry.encoding));
        }
        printf ("\n");
        p += entry.len;
        index ++;
    }
    printf ("{end}\n\n");
}

#ifdef REDIS_TEST
#include <sys/time.h>
#include "../lib/adlist.h"
#include "../lib/sds.h"

#define debug(f, ...) { if (DEBUG) printf(f, __VA_ARGS__); }

static unsigned char *createList ( )
{
    unsigned char *zl = ziplistNew ();
    zl = ziplistPush (zl, ( unsigned char* ) "foo", 3, ZIPLIST_TAIL);
    zl = ziplistPush (zl, ( unsigned char* ) "quux", 4, ZIPLIST_TAIL);
    zl = ziplistPush (zl, ( unsigned char* ) "hello", 5, ZIPLIST_HEAD);
    zl = ziplistPush (zl, ( unsigned char* ) "1024", 4, ZIPLIST_TAIL);
    return zl;
}

static unsigned char *createIntList ( )
{
    unsigned char *zl = ziplistNew ();
    char buf[32];

    sprintf (buf, "100");
    zl = ziplistPush (zl, ( unsigned char* ) buf, strlen (buf), ZIPLIST_TAIL);
    sprintf (buf, "128000");
    zl = ziplistPush (zl, ( unsigned char* ) buf, strlen (buf), ZIPLIST_TAIL);
    sprintf (buf, "-100");
    zl = ziplistPush (zl, ( unsigned char* ) buf, strlen (buf), ZIPLIST_HEAD);
    sprintf (buf, "4294967296");
    zl = ziplistPush (zl, ( unsigned char* ) buf, strlen (buf), ZIPLIST_HEAD);
    sprintf (buf, "non integer");
    zl = ziplistPush (zl, ( unsigned char* ) buf, strlen (buf), ZIPLIST_TAIL);
    sprintf (buf, "much much longer non integer");
    zl = ziplistPush (zl, ( unsigned char* ) buf, strlen (buf), ZIPLIST_TAIL);
    return zl;
}

static long long usec ( void )
{
    struct timeval tv;
    gettimeofday (&tv, NULL);
    return (( ( long long ) tv.tv_sec )*1000000 )+ tv.tv_usec;
}

static void stress ( int pos, int num, int maxsize, int dnum )
{
    int i, j, k;
    unsigned char *zl;
    char posstr[2][5] = { "HEAD", "TAIL" };
    long long start;
    for ( i = 0; i < maxsize; i += dnum )
    {
        zl = ziplistNew ();
        for ( j = 0; j < i; j ++ )
        {
            zl = ziplistPush (zl, ( unsigned char* ) "quux", 4, ZIPLIST_TAIL);
        }

        /* Do num times a push+pop from pos */
        start = usec ();
        for ( k = 0; k < num; k ++ )
        {
            zl = ziplistPush (zl, ( unsigned char* ) "quux", 4, pos);
            zl = ziplistDeleteRange (zl, 0, 1);
        }
        printf ("List size: %8d, bytes: %8d, %dx push+pop (%s): %6lld usec\n",
                i, intrev32ifbe (ZIPLIST_BYTES (zl)), num, posstr[pos], usec () - start);
        zfree (zl);
    }
}

static unsigned char *pop ( unsigned char *zl, int where )
{
    unsigned char *p, *vstr;
    unsigned int vlen;
    long long vlong;

    p = ziplistIndex (zl, where == ZIPLIST_HEAD ? 0 : - 1);
    if ( ziplistGet (p, &vstr, &vlen, &vlong) )
    {
        if ( where == ZIPLIST_HEAD )
            printf ("Pop head: ");
        else
            printf ("Pop tail: ");

        if ( vstr )
        {
            if ( vlen && fwrite (vstr, vlen, 1, stdout) == 0 ) perror ("fwrite");
        }
        else
        {
            printf ("%lld", vlong);
        }

        printf ("\n");
        return ziplistDelete (zl, &p);
    }
    else
    {
        printf ("ERROR: Could not pop\n");
        exit (1);
    }
}

static int randstring ( char *target, unsigned int min, unsigned int max )
{
    int p = 0;
    int len = min + rand () % ( max - min + 1 );
    int minval, maxval;
    switch ( rand () % 3 )
    {
        case 0:
            minval = 0;
            maxval = 255;
            break;
        case 1:
            minval = 48;
            maxval = 122;
            break;
        case 2:
            minval = 48;
            maxval = 52;
            break;
        default:
            assert (NULL);
    }

    while ( p < len )
        target[p ++] = minval + rand () % ( maxval - minval + 1 );
    return len;
}

static void verify ( unsigned char *zl, zlentry *e )
{
    int len = ziplistLen (zl);
    zlentry _e;

    ZIPLIST_ENTRY_ZERO (&_e);

    for ( int i = 0; i < len; i ++ )
    {
        memset (&e[i], 0, sizeof (zlentry ));
        zipEntry (ziplistIndex (zl, i), &e[i]);

        memset (&_e, 0, sizeof (zlentry ));
        zipEntry (ziplistIndex (zl, - len + i), &_e);

        assert (memcmp (&e[i], &_e, sizeof (zlentry )) == 0);
    }
}

int ziplistTest ( int argc, char **argv )
{
    unsigned char *zl, *p;
    unsigned char *entry;
    unsigned int elen;
    long long value;

    /* If an argument is given, use it as the random seed. */
    if ( argc == 2 )
        srand (atoi (argv[1]));

    zl = createIntList ();
    ziplistRepr (zl);

    zfree (zl);

    zl = createList ();
    ziplistRepr (zl);

    zl = pop (zl, ZIPLIST_TAIL);
    ziplistRepr (zl);

    zl = pop (zl, ZIPLIST_HEAD);
    ziplistRepr (zl);

    zl = pop (zl, ZIPLIST_TAIL);
    ziplistRepr (zl);

    zl = pop (zl, ZIPLIST_TAIL);
    ziplistRepr (zl);

    zfree (zl);

    printf ("Get element at index 3:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 3);
        if ( ! ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("ERROR: Could not access index 3\n");
            return 1;
        }
        if ( entry )
        {
            if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            printf ("\n");
        }
        else
        {
            printf ("%lld\n", value);
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Get element at index 4 (out of range):\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 4);
        if ( p == NULL )
        {
            printf ("No entry\n");
        }
        else
        {
            printf ("ERROR: Out of range index should return NULL, returned offset: %ld\n", p - zl);
            return 1;
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Get element at index -1 (last element):\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, - 1);
        if ( ! ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("ERROR: Could not access index -1\n");
            return 1;
        }
        if ( entry )
        {
            if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            printf ("\n");
        }
        else
        {
            printf ("%lld\n", value);
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Get element at index -4 (first element):\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, - 4);
        if ( ! ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("ERROR: Could not access index -4\n");
            return 1;
        }
        if ( entry )
        {
            if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            printf ("\n");
        }
        else
        {
            printf ("%lld\n", value);
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Get element at index -5 (reverse out of range):\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, - 5);
        if ( p == NULL )
        {
            printf ("No entry\n");
        }
        else
        {
            printf ("ERROR: Out of range index should return NULL, returned offset: %ld\n", p - zl);
            return 1;
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Iterate list from 0 to end:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 0);
        while ( ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("Entry: ");
            if ( entry )
            {
                if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            }
            else
            {
                printf ("%lld", value);
            }
            p = ziplistNext (zl, p);
            printf ("\n");
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Iterate list from 1 to end:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 1);
        while ( ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("Entry: ");
            if ( entry )
            {
                if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            }
            else
            {
                printf ("%lld", value);
            }
            p = ziplistNext (zl, p);
            printf ("\n");
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Iterate list from 2 to end:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 2);
        while ( ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("Entry: ");
            if ( entry )
            {
                if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            }
            else
            {
                printf ("%lld", value);
            }
            p = ziplistNext (zl, p);
            printf ("\n");
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Iterate starting out of range:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 4);
        if ( ! ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("No entry\n");
        }
        else
        {
            printf ("ERROR\n");
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Iterate from back to front:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, - 1);
        while ( ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("Entry: ");
            if ( entry )
            {
                if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            }
            else
            {
                printf ("%lld", value);
            }
            p = ziplistPrev (zl, p);
            printf ("\n");
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Iterate from back to front, deleting all items:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, - 1);
        while ( ziplistGet (p, &entry, &elen, &value) )
        {
            printf ("Entry: ");
            if ( entry )
            {
                if ( elen && fwrite (entry, elen, 1, stdout) == 0 ) perror ("fwrite");
            }
            else
            {
                printf ("%lld", value);
            }
            zl = ziplistDelete (zl, &p);
            p = ziplistPrev (zl, p);
            printf ("\n");
        }
        printf ("\n");
        zfree (zl);
    }

    printf ("Delete inclusive range 0,0:\n");
    {
        zl = createList ();
        zl = ziplistDeleteRange (zl, 0, 1);
        ziplistRepr (zl);
        zfree (zl);
    }

    printf ("Delete inclusive range 0,1:\n");
    {
        zl = createList ();
        zl = ziplistDeleteRange (zl, 0, 2);
        ziplistRepr (zl);
        zfree (zl);
    }

    printf ("Delete inclusive range 1,2:\n");
    {
        zl = createList ();
        zl = ziplistDeleteRange (zl, 1, 2);
        ziplistRepr (zl);
        zfree (zl);
    }

    printf ("Delete with start index out of range:\n");
    {
        zl = createList ();
        zl = ziplistDeleteRange (zl, 5, 1);
        ziplistRepr (zl);
        zfree (zl);
    }

    printf ("Delete with num overflow:\n");
    {
        zl = createList ();
        zl = ziplistDeleteRange (zl, 1, 5);
        ziplistRepr (zl);
        zfree (zl);
    }

    printf ("Delete foo while iterating:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 0);
        while ( ziplistGet (p, &entry, &elen, &value) )
        {
            if ( entry && strncmp ("foo", ( char* ) entry, elen) == 0 )
            {
                printf ("Delete foo\n");
                zl = ziplistDelete (zl, &p);
            }
            else
            {
                printf ("Entry: ");
                if ( entry )
                {
                    if ( elen && fwrite (entry, elen, 1, stdout) == 0 )
                        perror ("fwrite");
                }
                else
                {
                    printf ("%lld", value);
                }
                p = ziplistNext (zl, p);
                printf ("\n");
            }
        }
        printf ("\n");
        ziplistRepr (zl);
        zfree (zl);
    }

    printf ("Regression test for >255 byte strings:\n");
    {
        char v1[257] = { 0 }, v2[257] = { 0 };
        memset (v1, 'x', 256);
        memset (v2, 'y', 256);
        zl = ziplistNew ();
        zl = ziplistPush (zl, ( unsigned char* ) v1, strlen (v1), ZIPLIST_TAIL);
        zl = ziplistPush (zl, ( unsigned char* ) v2, strlen (v2), ZIPLIST_TAIL);

        /* Pop values again and compare their value. */
        p = ziplistIndex (zl, 0);
        assert (ziplistGet (p, &entry, &elen, &value));
        assert (strncmp (v1, ( char* ) entry, elen) == 0);
        p = ziplistIndex (zl, 1);
        assert (ziplistGet (p, &entry, &elen, &value));
        assert (strncmp (v2, ( char* ) entry, elen) == 0);
        printf ("SUCCESS\n\n");
        zfree (zl);
    }

    printf ("Regression test deleting next to last entries:\n");
    {
        char v[3][257] = {
            {0 } };
        zlentry e[3] = {
            {.prevrawlensize = 0, .prevrawlen = 0, .lensize = 0,
            .len = 0, .headersize = 0, .encoding = 0, .p = NULL } };
        size_t i;

        for ( i = 0; i < ( sizeof (v ) / sizeof (v[0] ) ); i ++ )
        {
            memset (v[i], 'a' + i, sizeof (v[0] ));
        }

        v[0][256] = '\0';
        v[1][ 1] = '\0';
        v[2][256] = '\0';

        zl = ziplistNew ();
        for ( i = 0; i < ( sizeof (v ) / sizeof (v[0] ) ); i ++ )
        {
            zl = ziplistPush (zl, ( unsigned char * ) v[i], strlen (v[i]), ZIPLIST_TAIL);
        }

        verify (zl, e);

        assert (e[0].prevrawlensize == 1);
        assert (e[1].prevrawlensize == 5);
        assert (e[2].prevrawlensize == 1);

        /* Deleting entry 1 will increase `prevrawlensize` for entry 2 */
        unsigned char *p = e[1].p;
        zl = ziplistDelete (zl, &p);

        verify (zl, e);

        assert (e[0].prevrawlensize == 1);
        assert (e[1].prevrawlensize == 5);

        printf ("SUCCESS\n\n");
        zfree (zl);
    }

    printf ("Create long list and check indices:\n");
    {
        zl = ziplistNew ();
        char buf[32];
        int i, len;
        for ( i = 0; i < 1000; i ++ )
        {
            len = sprintf (buf, "%d", i);
            zl = ziplistPush (zl, ( unsigned char* ) buf, len, ZIPLIST_TAIL);
        }
        for ( i = 0; i < 1000; i ++ )
        {
            p = ziplistIndex (zl, i);
            assert (ziplistGet (p, NULL, NULL, &value));
            assert (i == value);

            p = ziplistIndex (zl, - i - 1);
            assert (ziplistGet (p, NULL, NULL, &value));
            assert (999 - i == value);
        }
        printf ("SUCCESS\n\n");
        zfree (zl);
    }

    printf ("Compare strings with ziplist entries:\n");
    {
        zl = createList ();
        p = ziplistIndex (zl, 0);
        if ( ! ziplistCompare (p, ( unsigned char* ) "hello", 5) )
        {
            printf ("ERROR: not \"hello\"\n");
            return 1;
        }
        if ( ziplistCompare (p, ( unsigned char* ) "hella", 5) )
        {
            printf ("ERROR: \"hella\"\n");
            return 1;
        }

        p = ziplistIndex (zl, 3);
        if ( ! ziplistCompare (p, ( unsigned char* ) "1024", 4) )
        {
            printf ("ERROR: not \"1024\"\n");
            return 1;
        }
        if ( ziplistCompare (p, ( unsigned char* ) "1025", 4) )
        {
            printf ("ERROR: \"1025\"\n");
            return 1;
        }
        printf ("SUCCESS\n\n");
        zfree (zl);
    }

    printf ("Merge test:\n");
    {
        /* create list gives us: [hello, foo, quux, 1024] */
        zl = createList ();
        unsigned char *zl2 = createList ();

        unsigned char *zl3 = ziplistNew ();
        unsigned char *zl4 = ziplistNew ();

        if ( ziplistMerge (&zl4, &zl4) )
        {
            printf ("ERROR: Allowed merging of one ziplist into itself.\n");
            return 1;
        }

        /* Merge two empty ziplists, get empty result back. */
        zl4 = ziplistMerge (&zl3, &zl4);
        ziplistRepr (zl4);
        if ( ziplistLen (zl4) )
        {
            printf ("ERROR: Merging two empty ziplists created entries.\n");
            return 1;
        }
        zfree (zl4);

        zl2 = ziplistMerge (&zl, &zl2);
        /* merge gives us: [hello, foo, quux, 1024, hello, foo, quux, 1024] */
        ziplistRepr (zl2);

        if ( ziplistLen (zl2) != 8 )
        {
            printf ("ERROR: Merged length not 8, but: %u\n", ziplistLen (zl2));
            return 1;
        }

        p = ziplistIndex (zl2, 0);
        if ( ! ziplistCompare (p, ( unsigned char* ) "hello", 5) )
        {
            printf ("ERROR: not \"hello\"\n");
            return 1;
        }
        if ( ziplistCompare (p, ( unsigned char* ) "hella", 5) )
        {
            printf ("ERROR: \"hella\"\n");
            return 1;
        }

        p = ziplistIndex (zl2, 3);
        if ( ! ziplistCompare (p, ( unsigned char* ) "1024", 4) )
        {
            printf ("ERROR: not \"1024\"\n");
            return 1;
        }
        if ( ziplistCompare (p, ( unsigned char* ) "1025", 4) )
        {
            printf ("ERROR: \"1025\"\n");
            return 1;
        }

        p = ziplistIndex (zl2, 4);
        if ( ! ziplistCompare (p, ( unsigned char* ) "hello", 5) )
        {
            printf ("ERROR: not \"hello\"\n");
            return 1;
        }
        if ( ziplistCompare (p, ( unsigned char* ) "hella", 5) )
        {
            printf ("ERROR: \"hella\"\n");
            return 1;
        }

        p = ziplistIndex (zl2, 7);
        if ( ! ziplistCompare (p, ( unsigned char* ) "1024", 4) )
        {
            printf ("ERROR: not \"1024\"\n");
            return 1;
        }
        if ( ziplistCompare (p, ( unsigned char* ) "1025", 4) )
        {
            printf ("ERROR: \"1025\"\n");
            return 1;
        }
        printf ("SUCCESS\n\n");
        zfree (zl);
    }

    printf ("Stress with random payloads of different encoding:\n");
    {
        int i, j, len, where;
        unsigned char *p;
        char buf[1024];
        int buflen;
        list *ref;
        listNode *refnode;

        /* Hold temp vars from ziplist */
        unsigned char *sstr;
        unsigned int slen;
        long long sval;

        for ( i = 0; i < 20000; i ++ )
        {
            zl = ziplistNew ();
            ref = listCreate ();
            listSetFreeMethod (ref, ( void (* )( void* ) )sdsfree);
            len = rand () % 256;

            /* Create lists */
            for ( j = 0; j < len; j ++ )
            {
                where = ( rand () & 1 ) ? ZIPLIST_HEAD : ZIPLIST_TAIL;
                if ( rand () % 2 )
                {
                    buflen = randstring (buf, 1, sizeof (buf ) - 1);
                }
                else
                {
                    switch ( rand () % 3 )
                    {
                        case 0:
                            buflen = sprintf (buf, "%lld", ( 0LL + rand () ) >> 20);
                            break;
                        case 1:
                            buflen = sprintf (buf, "%lld", ( 0LL + rand () ));
                            break;
                        case 2:
                            buflen = sprintf (buf, "%lld", ( 0LL + rand () ) << 20);
                            break;
                        default:
                            assert (NULL);
                    }
                }

                /* Add to ziplist */
                zl = ziplistPush (zl, ( unsigned char* ) buf, buflen, where);

                /* Add to reference list */
                if ( where == ZIPLIST_HEAD )
                {
                    listAddNodeHead (ref, sdsnewlen (buf, buflen));
                }
                else if ( where == ZIPLIST_TAIL )
                {
                    listAddNodeTail (ref, sdsnewlen (buf, buflen));
                }
                else
                {
                    assert (NULL);
                }
            }

            assert (listLength (ref) == ziplistLen (zl));
            for ( j = 0; j < len; j ++ )
            {
                /* Naive way to get elements, but similar to the stresser
                 * executed from the Tcl test suite. */
                p = ziplistIndex (zl, j);
                refnode = listIndex (ref, j);

                assert (ziplistGet (p, &sstr, &slen, &sval));
                if ( sstr == NULL )
                {
                    buflen = sprintf (buf, "%lld", sval);
                }
                else
                {
                    buflen = slen;
                    memcpy (buf, sstr, buflen);
                    buf[buflen] = '\0';
                }
                assert (memcmp (buf, listNodeValue (refnode), buflen) == 0);
            }
            zfree (zl);
            listRelease (ref);
        }
        printf ("SUCCESS\n\n");
    }

    printf ("Stress with variable ziplist size:\n");
    {
        stress (ZIPLIST_HEAD, 100000, 16384, 256);
        stress (ZIPLIST_TAIL, 100000, 16384, 256);
    }

    return 0;
}
#endif
